package redis.clients.util;

/**
 * CRC16 Implementation according to CCITT standard Polynomial : 1021 (x^16 + x^12 + x^5 + 1) See <a
 * href="http://redis.io/topics/cluster-spec">Appendix A. CRC16 reference implementation in ANSI
 * C</a>
 */
public class JedisClusterCRC16 {
  private static final int LOOKUP_TABLE[] = { 0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5,
      0x60C6, 0x70E7, 0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF, 0x1231,
      0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6, 0x9339, 0x8318, 0xB37B, 0xA35A,
      0xD3BD, 0xC39C, 0xF3FF, 0xE3DE, 0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4,
      0x5485, 0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D, 0x3653, 0x2672,
      0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4, 0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF,
      0xE7FE, 0xD79D, 0xC7BC, 0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823,
      0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B, 0x5AF5, 0x4AD4, 0x7AB7,
      0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12, 0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58,
      0xBB3B, 0xAB1A, 0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41, 0xEDAE,
      0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49, 0x7E97, 0x6EB6, 0x5ED5, 0x4EF4,
      0x3E13, 0x2E32, 0x1E51, 0x0E70, 0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59,
      0x8F78, 0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F, 0x1080, 0x00A1,
      0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067, 0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D,
      0xD31C, 0xE37F, 0xF35E, 0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256,
      0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D, 0x34E2, 0x24C3, 0x14A0,
      0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E,
      0xC71D, 0xD73C, 0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634, 0xD94C,
      0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB, 0x5844, 0x4865, 0x7806, 0x6827,
      0x18C0, 0x08E1, 0x3882, 0x28A3, 0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB,
      0xBB9A, 0x4A75, 0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92, 0xFD2E, 0xED0F,
      0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9, 0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2,
      0x2C83, 0x1CE0, 0x0CC1, 0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8,
      0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0, };

  public static int getSlot(String key) {
    int s = key.indexOf("{");
    if (s > -1) {
      int e = key.indexOf("}", s + 1);
      if (e > -1 && e != s + 1) {
        key = key.substring(s + 1, e);
      }
    }
    // optimization with modulo operator with power of 2
    // equivalent to getCRC16(key) % 16384
    return getCRC16(key) & (16384 - 1);
  }

  public static int getSlot(byte[] key) {
    int s = -1;
    int e = -1;
    boolean sFound = false;
    for (int i = 0; i < key.length; i++) {
      if (key[i] == '{' && !sFound) {
        s = i;
        sFound = true;
      }
      if (key[i] == '}' && sFound) {
        e = i;
        break;
      }
    }
    if (s > -1 && e > -1 && e != s + 1) {
      return getCRC16(key, s + 1, e) & (16384 - 1);
    }
    return getCRC16(key) & (16384 - 1);
  }

  /**
   * Create a CRC16 checksum from the bytes. implementation is from mp911de/lettuce, modified with
   * some more optimizations
   * @param bytes
   * @return CRC16 as integer value See <a
   *         href="https://github.com/xetorthio/jedis/pull/733#issuecomment-55840331">Issue 733</a>
   */
  public static int getCRC16(byte[] bytes, int s, int e) {
    int crc = 0x0000;

    for (int i = s; i < e; i++) {
      crc = ((crc << 8) ^ LOOKUP_TABLE[((crc >>> 8) ^ (bytes[i] & 0xFF)) & 0xFF]);
    }
    return crc & 0xFFFF;
  }

  public static int getCRC16(byte[] bytes) {
    return getCRC16(bytes, 0, bytes.length);
  }

  public static int getCRC16(String key) {
    byte[] bytesKey = SafeEncoder.encode(key);
    return getCRC16(bytesKey, 0, bytesKey.length);
  }
}
